The main aim of this projects is to study the regulation of energy expenditure and energy intake in humans and identify metabolic risk factors of weight gain in children and adults. To assess resting energy expenditure we use indirect calorimetry (metabolic carts and respiratory chamber). To assess energy expenditure in free-living condition we use doubly labeled water DWL). To assess energy intake and eating behavior we use food frequency questionnaires, vending machines, and taste tests. To determine the neuroanatomical correlates of hunger, taste and satiation we use positron emission tomography (PET). In the past year we have: a)extended the 5-y follow up to 230 10 y old Pima Indian children, now including 27 offspring of diabetic mothers, to identify risk factors of childhood obesity and insulin resistance; b)expanded the study of the heritability of physical activity level (PAL) from 70 to 94 pairs of twins; c)initiated a collaborative study to validate diet and PAL questionnaires in 35 Native American children using DLW; d)initiated a study to characterize eating behavior in pre-pubertal offspring of diabetic mothers; e)initiated a study to identify heritable aspects of eating behavior in adult Pima siblings; f) characterized brain responses to a meal in 10 lean and 12 obese women; g)completed PET study in 11 post-obese individuals; h)initiated PET study in individuals with Prader-Willi syndrome